The invention relates to the field of forming and maintaining the structural integrity of crystalline/buried oxide dielectric stacks.
Dielectric stacks composed of semiconductor crystalline layers and their oxide are found in a variety of devices such as Vertical Cavity Surface Emitting Lasers (VCSELs), saturable Bragg reflectors (SBRs), and photonic crystals. Although both VCSELs and SBRs employ alternating layers of high and low indices of refraction, the purpose of the oxide in the structures are typically different. In VCSELs, the selective oxidation of AlAs to form AlxOy is used to create current apertures as well as to increase the optical mode's lateral confinement. In SBRs, the selective oxidation of AlAs is used to increase the index contrast in the dielectric mirror stack. By increasing the index contrast, fewer pairs of high index material and AlxOy are required to achieve the desired reflectivity while at the same time increasing the high reflectivity bandwidth of the dielectric mirror stack.
During the formation of the AlxOy from either AlAs or high aluminum content AlGaAs, the final structure, whether it is a SBR, VCSEL or even a photonic crystal structure, can experience delamination at the buried oxide/crystalline material interface. The crystalline material, which is almost always the high index material, can consist of arsenide, phosphide, antimonide, or dilute nitride-based III-V material. The exact thickness of the oxide layers and the crystalline layers depend on the application. In the case of SBRs, the thickness of the oxide layers and the crystalline III-V material in the dielectric mirror stack is λ/4n where n is the index of refraction of the respective material and λ is the wavelength of operation. In addition, the extent of the oxidation is on the order of several 100's of nanometers. In the case of VCSELs, the thickness of the oxide layer that is used as a current aperture is significantly less than λ/4n and the oxidation extent is typically a few 10's of nanometers. In the case of photonic crystals, the thickness of the single buried oxide layers is on the order of λ/n in order to optically isolate the high index material that is used in the photonic crystal from the high index substrate material.